nozzle stage for a turbine engine

ABSTRACT

A nozzle stage for a turbine engine includes two substantially cylindrical rings, respectively an inner ring and an outer ring, with, extending between them: vanes carried by a first one of the rings; vanes carried by the second ring; and spacer-forming vanes interconnecting the two rings; the vanes of the first and second rings being arranged in alternation.

The present invention relates to a nozzle stage for a compressor or aturbine of a turbine engine such as an airplane turboprop or turbojet.

A nozzle stage of this type comprises two substantially cylindricalrings extending one inside the other with substantially radial vanesextending between them.

A nozzle stage is generally a single piece and it may be made by castingor by machining (e.g. electrical discharge machining (EDM)), or byassembling and welding each vane to the rings.

Nevertheless, under such circumstances, the length of time required forfabricating a nozzle stage is relatively long. Furthermore, when thenozzle stage has a high density of vanes, i.e. when its vanes are closetogether in the circumferential direction, the above-mentionedfabrication techniques are difficult or even impossible to implement.When a tool is used for machining a nozzle vane or for welding said vaneto the rings, the tool needs to be passed between two consecutive vanesof the stage, and that is not always possible when the circumferentialpitch between two consecutive vanes is very small.

A particular object of the invention is to provide a solution to thoseproblems that is simple, effective, and inexpensive.

The invention provides a nozzle stage, e.g. having a high density ofvanes, that is easier to make than prior art nozzle stages, while usingfabrication techniques that are simpler, faster, and less expensive.

To this end, the invention provides a nozzle stage for a turbine engine,the stage comprising two substantially cylindrical rings, respectivelyan inner ring and an outer ring, with substantially radial vanesextending between them, the stage being characterized in that itcomprises a first series of vanes carried by a first one of the rings, asecond series of vanes carried by the second ring, and connection meansinterconnecting the two rings, the vanes of the first and second ringsbeing arranged in alternation.

Advantageously, the ring connection means comprise spacer vanes havingtheir ends fastened to the first and second rings, respectively.

The nozzle stage of the invention thus essentially comprises two seriesof vanes together with connecting spacer vanes: a first series of vanesconnected to the first ring and independent from the second ring; asecond series of vanes connected to the second ring and independent ofthe first ring, with each vane of the second ring extending between twovanes of the first ring; and spacer vanes that are connected to bothrings and that serve to hold together the parts of the nozzle stage.

Each ring thus carries approximately only half of the vanes of thestage, thereby doubling the inter-vane pitch and facilitating access tosaid vanes for the above-mentioned machining or welding tools, and thusmaking it easier to fabricate the nozzle stage.

The vanes of each series are preferably substantially regularlydistributed around the longitudinal axis of the stage.

The circumferential pitch between two consecutive vanes of the firstseries is thus substantially equal to the circumferential pitch betweentwo consecutive vanes of the second series and is substantially equal totwice the circumferential pitch of the vanes of a nozzle stage havingthe same density of vanes in the prior art. By way of example, thecircumferential pitch between two consecutive vanes carried by one ofthe rings may be approximately 27 millimeters (mm) and thecircumferential pitch between two consecutive vanes of the assembledstage may be approximately 13.5 mm.

According to another characteristic of the invention, the vanes of thefirst series have free ends that are flush with or at a short radialdistance from the second ring, and the vanes of the second series havefree ends that are flush with or at a short radial distance from thefirst ring. The radial distance between the free end of each vane of thesecond and third series and the corresponding ring is advantageouslyless than or equal to 0.05 mm, in such a manner as to avoid disturbingthe flow of the stream of air between the rings of the stage.

Preferably, each ring is sectorized and comprises at least two annularsectors mounted end to end. Each annular sector of a ring may be formedas a single piece with the vanes that are carried by the ring sector,and may be made by casting or by machining, for example.

In a variant, the vanes carried by each annular sector of a ring arefitted thereto, being fastened to the ring sector, e.g. by brazing orwelding.

According to another characteristic of the invention, the spacer vanesare connected to the rings in releasable manner. The radially outer endof each spacer vane may be threaded and may be engaged in a radialorifice of the outer ring and to receive a nut that bears against saidouter ring.

The nozzle stage may also include an annular rail mounted on the innerring and including an outer annular groove in which an inner annular rimof each sector of the inner ring and the radially inner end of eachspacer vane are engaged by sliding in the circumferential direction.

Finally, the invention provides a turbine engine such as an airplaneturboprop or turbojet, characterized in that it includes at least onenozzle stage as described above.

The invention can be better understood and other characteristics,details, and advantages thereof appear more clearly on reading thefollowing description made by way of non-limiting example and withreference to the accompanying drawings, in which:

FIG. 1 is a fragmentary diagrammatic view in perspective of a nozzlestage of the invention;

FIG. 2 is a fragmentary diagrammatic view in perspective of the outerring of the FIG. 1 nozzle stage;

FIG. 3 is a diagrammatic view in perspective and on a larger scaleshowing the fastening of a spacer vane to the outer ring of FIG. 2; and

FIGS. 4 and 5 are fragmentary diagrammatic views in perspective and on alarger scale of the nozzle stage of the invention.

FIG. 1 shows a portion of a nozzle stage 10 of the invention, comprisingtwo coaxial rings 12 and 14, respectively an inner ring and outer ring,with substantially radial vanes 16, 18, and 20 extending between them,the rings 12 and 14 and the vanes 16, 18, and 20 being described ingreater detail below with reference to FIGS. 2 to 5.

This nozzle stage 10 forms part of a turbine or a compressor in aturbine engine. It forms a stator element of the turbine or thecompressor and it is arranged between two rotor stages of the turbine orthe compressor, each of which is formed by a rotor wheel having anannular row of blades.

In the example shown, the nozzle stage 10 comprises two annular portionseach occupying about 180° (only one of which is shown), these twoportions being arranged end to end circumferentially and fastenedtogether by appropriate means, e.g. of the nut-and-bolt type.

The portion of the nozzle stage 10 that is shown comprises an annularsector 15 of the outer ring 14 (extending over about 180°) and threeannular sectors 13 of the inner ring 12 (each extending over about 55°to 60°, which sectors are arranged circumferentially end to end. FIG. 2is a diagrammatic perspective view of the sector 15 of the outer ring14.

This sector 15 carries a first series of vanes 16 that are connected viatheir radially outer ends to a cylindrical wall 22 of the sector.

These vanes 16 are regularly distributed around the longitudinal axis ofthe nozzle stage and they are spaced apart from one another at acircumferential pitch K. The vanes 16 carried by the sector 15 may bethirty in number, for example.

The vanes 16 may be formed integrally with the sector 15 or they may befittings that are fastened via their radially outer ends to thecylindrical wall 22 of the sector 15.

The ring sector 15 also includes an annular wall 24 extending radiallyoutwards for mounting the nozzle stage 10 in the turbine or thecompressor of the turbine engine.

The cylindrical wall 22 of the ring sector 15 includes substantiallyradial orifices 28 in which the radially outer ends of spacer-formingvanes 20 are engaged, which vanes serve to connect the two rings 12 and14 securely together.

In the example shown in FIG. 1, these spacer vanes 20 are four in numberand they are regularly distributed around the longitudinal axis of thestage. Amongst these four spacer vanes 20, two are situated at thecircumferential ends of the ring sector 15. The other two vanes 20 ofthe ring sector 15 are situated at a distance from the circumferentialends of the sector, each being arranged between two consecutive vanes 16carried by the sector.

The fastening of a vane 20 is shown on a larger scale in FIG. 3.

At its radially outer end, the vane 20 has a cylindrical stud 26 that isengaged in an orifice 28 in the cylindrical wall 22 of the ring sector15 and that has its radially outer portion threaded so as to receivefrom the outside a nut 30 that is to bear against the outside surface ofthe wall 22 of the ring sector 15, either directly or via a washer 32.

At its radially inner end, the vane 20 includes a platform 34 that isconnected to a root 36 that is substantially I-shaped in section (in aplane containing the longitudinal axis of the stage).

Each vane 20 is mounted on the ring sector 15 by being moved radially intranslation from the inside towards the outside until its stud 26 isengaged in one of the orifices 28 of the ring sector 15. The nut 30 isthen screwed onto the threaded portion of the stud and is tightenedagainst the ring sector so as to hold the vane 20 stationary in a radialdirection on the ring sector 15.

FIGS. 4 and 5 show another step in mounting the nozzle stage 10 of theinvention, in which each sector 13 of the inner ring 12 is arrangedbetween two platforms 34 of spacer vanes 20.

Each sector 13 of the inner ring carries a series of vanes 18 thatextend radially outwards from an outer cylindrical surface of thesector. Each sector 13 carries nine vanes 18 in the example shown. Eachof these vanes 18 is arranged between two consecutive vanes 16 of thesector 15 of the outer ring, or between one of those vanes 16 and aspacer vane 20.

The vanes 18 may be formed integrally with the corresponding ring sector13 or they may be fitted thereto, being fastened to said sector viatheir radially inner ends.

Each inner ring sector 13 is mounted on the outer ring as follows. Thesector 13 is aligned with the outer ring 15 and is placed at an axialdistance therefrom, and it is then moved in axial translation towardsthe sector 15, until the vanes 18 of the sector 13 are between the vanes16 of the sector 15.

In this position, the circumferential pitch between a vane 18 of thesector 13 and a vane 16 of the sector 15 is equal to K/2.

The free ends of the vanes 18 are flush with or at a short radialdistance from the ring sector 15, and the free ends of the vanes 16 areflush with or at a short radial distance from the ring sector 13. Thesedistances are preferably less than or equal to 0.05 mm. Each inner ringsector 13 is aligned in a circumferential direction with the platforms34 of the adjacent spacer vanes 20 and presents a section in a planecontaining the longitudinal axis of the stage that is of a shape that isidentical to the shape of the platforms 34 and of the roots 36 of thespacer vanes 20.

An annular rail 40 (shown in FIGS. 1, 4, and 5) extending over about180° serves to fasten the sectors 13 of the inner ring 12 securely tothe spacer vanes 20.

This rail 40 has an outer annular groove 42 of section that is of ashape that is substantially complementary to the shape of the roots 36of the vanes 20 and of the ring sectors 13. The roots of the vanes 20co-operate with the side walls of the grooves 42 in the rail to preventthe vanes turning about their axes, and they are held radially byannular rims 44 that extend towards each other from the side walls ofthe groove 42.

The roots 36 of the vanes 20 and each sector 13 are engaged by slidingin the circumferential direction into the annular groove 42 of the rail,by moving the rail 40 in the circumferential direction over the sectors13 of the inner ring 12 and over the root 36 of the vanes 20.

For this purpose, the root 36 of a vane 20 that is located at one of thecircumferential ends of the ring sector 15 is engaged in acircumferential end of the groove 42 of the rail 40, and then the railis moved in sliding in the circumferential direction over the sectors 13of the inner ring until the circumferential ends of the rail aresubstantially in radial alignment with the circumferential ends of thering sector 15.

At its inner periphery, the rail 40 may carry an annular element 46 ofabradable material that is to co-operate in friction with annular wiperscarried by the rotor of the turbine or the compressor so as to form alabyrinth type seal.

The first and second portions of the nozzle stage are identical andassembled in the same manner. These two portions are then placed end toend and fastened securely to each other in order to form the nozzlestage.

In the example shown in the drawings, the portion shown of the nozzlestage 10 comprises thirty vanes 16 of the first series, twenty-seven(=3×9) vanes 18 of the second series, and four spacer vanes 20. Thesecond portion (not shown) of this stage 10 is identical.

It is possible advantageously to interpose an undulating spring-formingblade 48 between the bottom of the root 36 of the vane 20, the base ofthe sector 13, and the bottom 50 of the groove 42 in the rail 40 (FIG.5) in order to ensure continuous contact between the root 36 of the vane20 and the corresponding portion of each sector 13 with the rims 44 ofthe groove 42 in the rail 40.

The radial heights of the rims 44 of the groove 42 in the rail aredetermined relative to the radial dimensions of the connections betweenthe roots 36 of the vanes 20 and their platforms 34 so as to obtain asnug fit of the roots of the vanes 20 in the groove 42 in the rail, andlikewise for the corresponding portions of the sectors 13. As a result,the outside faces of the platforms 34 of the vanes 20 and thecorresponding portions of the sectors 13 are at exactly the same level,thereby ensuring continuity of the inside surface defining the passagefor fluid flow through the nozzle stage.

1-13. (canceled)
 14. A nozzle stage for a turbine engine, the stagecomprising: two substantially cylindrical rings, of respectively aninner ring and an outer ring, with substantially radial vanes extendingbetween them; a first series of vanes carried by a first one of therings; a second series of vanes carried by the second ring; andconnection means interconnecting the two rings, the vanes of the firstring alternating with the vanes of the second ring.
 15. A nozzle stageaccording to claim 14, wherein the vanes of each series aresubstantially regularly distributed around the longitudinal axis of thestage.
 16. A nozzle stage according to claim 14, wherein the ringconnection means comprises spacer vanes having their ends fastened tothe first ring and to the second ring, respectively.
 17. A nozzle stageaccording to claim 14, wherein each ring is sectorized and comprises atleast two annular sectors mounted end to end.
 18. A nozzle stageaccording to claim 16, wherein each ring is sectorized and comprises atleast two annular sectors mounted end to end, and further comprising anannular rail mounted on the inner ring and including an outer annulargroove in which an inner annular rim of each sector of the inner ringand the radially inner end of each spacer vane are engaged by sliding inthe circumferential direction.
 19. A nozzle stage according to claim 18,further comprising undulating spring-forming blades interposed between abottom of the annular groove in the rail and both the sectors of theinner ring and roots of the spacer vanes.
 20. A nozzle stage accordingto claim 14, wherein the vanes of the first series have free ends thatare flush with or at a short radial distance from the second ring, andthe vanes of the second series have free ends that are flush with or ata short radial distance from the first ring.
 21. A nozzle stageaccording to claim 20, wherein the radial distance between the free endof each vane of the first and second series and the corresponding ringis less than or equal to 0.05 mm.
 22. A nozzle stage according to claim17, wherein each annular sector of a ring is formed integrally with thevanes carried by the ring sector.
 23. A nozzle stage according to claim17, wherein the vanes carried by each annular sector of a ring arefitted thereto, being fastened to the ring sector.
 24. A nozzle stageaccording to claim 16, wherein the spacer vanes are connected to therings in a releasable manner.
 25. A nozzle stage according to claim 16,wherein the radially outer end of each spacer vane is threaded and isengaged in a radial orifice of the outer ring and receives a nut thatbears against the outer ring.
 26. A nozzle stage according to claim 22,wherein each annular sector of a ring is formed by casting or bymachining with the vanes carried by the ring sector.
 27. A nozzle stageaccording to claim 23, wherein the vanes carried by each annular sectorof a ring are fastened thereto by brazing or welding.
 28. A turbineengine, comprising: at least one nozzle stage according to claim 14.